Sound on film recording



Aug. 5, 1941. G. L. DIMMICK ND 0N FILM nficonome Filed March 29, 1938 2 sheets sheet l umlll lm m n n M Aug. 5, 1941. L. DIMMICK 2,251,665

SOUND 0N FILM RECORDING Filed March 29, 1938 2- Sheets-Sheet 2 Jnnmtor Patented Aug. 5, 1941 UNETED STATS s ries SOUND N FELM RECORDING Glenn L. Dimmick, Haddonfield, N. J., assignor to Radio Corporation of America, a corporation of Delaware Claims.

The present invention relates to sound on film recording, and more particularly to a type of such recording which produces a double density direct positive.

The apparatus and method are improvements on my application Serial No. 168,173, filed October 9, 1937, entitled Production of sound records, which pertains to the direct recording of the positive film, and my application Serial No. 125,544, filed February 13, 1937, entitled Antiground noise recording system, which latter application discloses a type of double density recording.

Before proceeding with the description of my invention, it is desirable to define some of the terms hereinafter used in view of the fact that the ordinary photographic and sound recording terminology as applied to my invention may be somewhat confusing. I-Ieretofore, sound recording apparatus produced What was correctly termed a negative record, and this term was correct from both the photographic and sound recording standpoints, since the record produced by the recorder, like the record produced by a photographic camera, was printed onto a second record which, in turn, was adapted to be played in the film phonograph or sound picture apparatus, this second record being termed the print or positive. In the present apparatus I produce in the recorder a record which is adapted to be played in the film phonograph without the production of a large quantity of ground noise such as would be produced in the prior art original recordings. This record can be printed to produce a record corresponding to the prior art negative, although this latter record is, photographically speaking, a positive. On the other hand, the original record produced with my apparatus may be played back on a film phonograph and rerecorded to produce a record corresponding to the negative record of the prior art. Also, my direct positive record may be printed by what is known as the reversal process so as to produce a direct duplicate of itself adapted to be played in a sound reproducer.

For the foregoing reasons, it appears desirable to define the terminology used in this application, and I, accordingly, define these terms in accordance with the use of the record in sound recording and reproduction rather than with a View to photographic accuracy.

The original recording which is, from the photographic viewpoint, necessarily a negative, I refer to as a direct positive since it functions as a positive print in the sound reproducer. A

print from this direct positive which, photographically, is a positive, I refer to as a printed negative since, if reproduced in a film phonograph, it exhibits the characteristics of a prior art negative sound record. A print obtained from this printed negative and having the characteristics of the direct positive is referred to as a printed positive, and a print from the direct positive producing a positive by reversal is referred to as a reversal positive. By a double density record, I refer to a record wherein the sound waves are outlined in one density, while the opaque background corresponding to the envelope of those sound waves appears in a greater density.

My present invention is an improvement over the inventions of my prior applications referred to above in that it permits the recording of a double density direct positive record with a single optical system and with a simpler apparatus including much smaller number of parts.

One object of my invention is to provide an improved apparatus for making a direct positive sound record.

Another object of my invention is to provide an improved apparatus for making a double density sound record.

Another object of my invention is to provide an improved apparatus for making a double density direct positive sound record.

Another object of my invention is to provide an improved optical system for sound recording apparatus. Another object of my invention is to provide an improved ground noise reduction shutter arrangement in a recording optical system.

Another object of my invention is to provide an improved delay action mechanism for producing a double exposure.

Other and incidental objects of my invention will be apparent to those skilled in the art from a reading of the following specification and an inspection of the accompanying drawings, in which-- Figure 1 is a perspective view of my improved optical system;

Figure 2 is a View of the slit plate of the optical system of Fig. 1 taken from the right hand side of Fig. 1;

Figure 3 is a view of the sound record film produced by the apparatus of Figs. 1 and 2;

Figurel corresponds to Fig. 2 but shows a modified form of shutter and light aperture as projected on the slit plate adapted to produce a class A pushpull sound record;

Figure 5 shows the sound record produced by the modified apparatus shown in Fig. 1;

Figure 6 corresponds to Figs. 2 and 4 but shows a modified form of shutter and aperture for producing a class B pushpull sound record; and

Figure 7 shows the class B pushpull sound record produced by the apparatus of Fig. 6.

Referring first to Fig. 1, light from the source I passes through the condenser lens II to the aperture plate [2 which is provided with an aperture having a triangular portion 53 and a rectangular portion id for purposes hereinafter described. Light passing through the aperture [3-44 passes through the lens I5 which in cooperation with the lens ll focuses an image of the filament of the lamp [0 on the galvanometer mirror Hi. This galvanometer mirror [6 is vibrated in accordance with the sound impulses to be recorded. Light refiected from the mirror l6 passes through the lens I! which in cooperation with the lens l5 focuses an image of the aperture l3l:l on the slit plate l8. Light passing through the slits in the slit plate i8 is focused upon the film 23 by the objective 24 in the usual manner.

The slit plate is is provided as shown in the elevation in Fig. 2 with the usual sound recording slit 2| and the additional and wider slit 22. The triangular portion it of the aperture produces the image I3A on the slit 2i and this image is vibrated back and forth across the slit 2| by the galvanometer iii in accordance with the sound waves to be recorded.

The rectangular portion [4 of the aperture forms the rectangular image MA covering the slit 22 and although this image is vibrated by the galvanometer mirror It it is of such size that the slit 22 is illuminated at all times.

The ground noise reduction shutter 19 is actuated by the motor 26 in the customary manner in accordance with the envelope of the sound Waves as shown and described, for example, in McDowell Patent No. 1,856,197 but in the reverse manner, i. e., the shutter !9 covers the portion of the slit 22 corresponding to the area on the film .23 on which sound is to be recorded. The result of this is that the central and end portions of the slit 22 produce an auxiliary exposure on the sound track area on the film 23 following the envelope of the sound waves but deeply exposing this portion of the film, as indicated at 25 and 26 in Fig. 3.

As the triangular portion lZiA of the recording beam is vibrated across the slit 2! it produces the sound wave record indicated at 2'! in 3' of a less density than the portions 25 and 26. This portion 2'! is so exposed and developed as to produce the optimum value in the sound record. i. e. a minimum amount of zero shift distortion is produced. The exposure of the portions 25 and 25 is so predetermined by the width of the slit 22 which is not limited by the sound frequencies to be recorded but is limited only by the envelope of those sound frequencies that these portions of the film will be of an intense black. As a consequence, only dust or other foreign material on the surface of the film will be insufilcient to produce clear spots on the direct positive and a minimum of ground noise from the black portion of the film will be produced.

Since the slit 22 is located above the slit 2| and the film 23 in the recording apparatus moves in a downward direction, the image of the unobstructed portions of the slit 22 will be thrown on the film at a point below the image of the slit 2! by reason of the image reversal produced by the lens 24 and this image of the slit 22 will be projected on the film at a time subsequent to the sound vibrations being recorded by an amount determined by the spacing of these images. The ordinary rectifying amplifier used in a ground noise reduction circuit necessarily produces a time delay corresponding to the filtering action in this amplifier and the arrangement above described permits me to project this background envelopes on the sound record with a delay corresponding to this delay in the amplifier, so that the envelope portions 25 and 25 in the sound record are exactly synchronized on the record with the corresponding sound wave records.

It will be apparent to those skilled in the art that the record shown in Fig. 3 may be played directly on a film phonograph or other sound reproducer with a minimum of ground noise and may be correspondingly re-recorded as an ordinary negative from which prints can be made. On the other hand, the direct positive may be printed to a corresponding negative producing a minimum of exposed areas in the portions 25 and 26 and with a very dense exposure on the portion 28 which is unexposed in the direct positive while providing the proper intermediate exposure in the portions corresponding to the margins of the portion 27. I prefer, however, to either re-record this film to the customary type of negative or to print it by reversal so as to produce a reversal positive corresponding exactly with this direct positive. This procedure avoids any deficiencies in the print which might be caused by dirt or dust on the direct positive in the printing operation.

In the form of the invention shown in Fig. 4, the ground noise reduction shutter 59 is provided with an intermediate straight portion 33 separating the two triangular portions and the shutter is so adjusted that this part 38 never passes the slit 22, thereby always maintaining a black line 3! in the middle of sound record shown in Fig. 5. In this form of the invention the'aperture is not provided with a triangular portion B but is provided with a parallelogram I313, the vibration of which causes the ends of the image to move in complementary fashion back and forth across the slit providing a class A push-pull sound record as described and claimed in my Patent No. 2,109,452, issued March 1, 1938. The record in the present case, however, is a direct positive instead of a negative such as is produced in the said application.

In the form of the invention shown in Fig. 6, a ground noise reduction shutter is provided with the intermediate portion 39 as in Fig. 4 for producing the black dividing line 3| between the two portions of the sound record and the aperture is provided with a rectangular portion 16 as described before. In this form of the invention, however, additional apertures 32, 33 and 34 are provided which produce a direct positive class B push-pull sound record in the manner described and claimed in my application Serial No, 168,173 referred to above, this record being shown in Fig. '7. In the record shown in Fig. 7 the blackened portions 25 and 2G correspond to those in Fig. 5 while the portions of intermediate density 21 define the push-pull sound record, light being transmitted through the clear portions 28. 7

Having now described my invention, I claim:

1. The method of making a photographic sound record including the steps of projecting a beam of light of predetermined intensity upon a sound record in the form of a narrow line, varying the length of portions of said line in accordance with the sound waves to be recorded while maintaining the average length of said portions constant and superposing on the exposed portions of said record a second exposure corresponding to the envelope of the sound waves to be recorded.

2. The method of making a photographic sound record including the steps of projecting a beam of light of predetermined intensity upon a sound record in the form of a narrow line, varying the length of portions of said line in accordance with the sound Waves to be recorded while maintaining the average length of said portions constant and subsequently superposing on the exposed portions of said record a second exposure corresponding to the envelope of the sound waves to be recorded.

3. Sound recording apparatus including means for simultaneously projecting two narrow lines of light from a single source transversely and in partly overlapping relation upon a movable film, means for varying one of said lines in accordance with the sound waves to be recorded while maintaining the average length of said line constant, and means for varying the length of the overlapping portion of the other of said lines in accordance with the envelope of the sound waves to be recorded, and for simultaneously varying the length of the non-overlapping portion of said other line in accordance with the envelope of the sound waves to be recorded.

4. In sound recording apparatus of the class described, means providing an aperture having a rectangular portion and a contiguous portion of predeterminedly varying contour, means for directing a beam of light through said aperture, means for vibrating said beam of light in accordance with sound waves to be recorded, means for directing said beam of light in the form of an image of said aperture upon a slit plate having two adjacent slits in such a manner that one of said slits is illuminated by the rectangular portion of said beam and the other of said slits is illuminated by the contoured portion of said beam, means for intercepting predetermined portions of the light passing through the first of said slits in accordance with the envelope of the sound waves to be recorded, and means for imaging both of said slits in spaced relation upon a film.

5. In sound recording apparatus of the class described, means providing an aperture having a rectangular portion and a contiguous portion of predeterminedly varying contour, means for directing a beam of light through said aperture, means for vibrating said beam of light in accordance with sound waves to be recorded, means for directing said beam of light in the form of an image of said aperture upon a slit plate having two adjacent slits in such a manner that one of said slits is continuously illuminated by the rectangular portion of said beam and the other of said slits is illuminated by the contoured portion of said beam, means for intercepting predetermined portions of the light passing through the first of said slits in accordance with the envelope of the sound waves to be recorded, and means for imaging both of said slits in spaced relation upon a film.

GLENN L. DIMMICK. 

